This Small Business Innovation Research Phase 1 project aims to develop and characterize a novel Magnetic Exosomal Assay to isolate and detect single intact exosome concentrations in human serum. This proposed research will also evaluate the diagnostic potential of the Magnetic Exosomal Assay for diseases with impaired vascular integrity. Vascular integrity or the maintenance of blood vessel continuity is a fundamental process maintained through endothelial cell-cell junctions. Defects in endothelial barrier function are an initiating factor in several disease processes including atherosclerosis, ischemia/reperfusion, tumor angiogenesis, cancer metastasis, diabetes, sepsis and acute lung injury. An initial event in impaired vascular integrity is a dramatic increase in a novel type of extracellular vesicle (EV) from endothelial cells (EC) called exosomes. Therefore, the development of a highly sensitive, reproducible and easy-to- implement assay to detect exosome concentrations in complex clinical samples can have potential diagnostic and therapeutic benefit. In this research proposal, we will develop and characterize a novel Magnetic Exosomal Assay kit and reader for fast isolation and detection of single intact exosome concentrations in human serum. In addition, we will assess the optimized Magnetic Exosomal Assay on Community-Acquired Pneumonia patient serum. The ultimate goal of this research is to develop a highly sensitive, reproducible and easy to implement exosomal assay as a diagnostic tool for patients with various types of impaired vascular integrity-related diseases.